MEMS microphones (MEMS=Micro-Electro-Mechanical System) usually comprise a membrane/backplate pair that is arranged on the microphone's MEMS chip or in a cavity in the chip.
MEMS microphones are known, e.g., from U.S. Pat. No. 6,522,762, U.S. Pat. No. 6,781,231, or U.S. Pat. No. 6,732,588.
The volume between the sound inlet and the membrane/backplate pair is the front volume of the microphone. A large front volume decreases the microphone's performance and deteriorates the high audio frequency performance of a microphone. A small front volume can be obtained when the membrane/backplate pair is arranged near the sound inlet. However, a close proximity to the sound inlet increases the probability of the pair being destroyed by objects or by matter entering the sound inlet.
Another possibility of reducing the front volume is realized by arranging the pair at the bottom side of the MEMS chip and reducing the chip's thickness. However, then, the mechanical stability of the chip is jeopardized, although a thin chip is generally preferred following the present trend towards miniaturization of electric components.
Further, it is possible to arrange the membrane/backplate pair at the bottom side of the MEMS chip and provide a protection element, e.g., a grid as shown in U.S. Pat. No. 6,522,762, placed onto the upper side of the chip covering the sound inlet.